1. Field of the Invention
The present invention relates to an image recording apparatus and an image recording method, and more particularly, to an image recording apparatus and an image recording method for writing an image onto a recording medium having a reversible thermal recording layer.
2. Description of the Related Art
As a material effective for recording media capable of multicolor recording and erasure, a cholesteric liquid crystal compound with a molecular weight of approximately 1000 has previously been known (see Japanese Laid-open Patent Application No. H11-24027). This type of cholesteric liquid crystal compound selectively reflects only a specific wavelength in a liquid crystal phase temperature region, and the selectively reflected wavelength varies according to the temperature. The condition where the cholesteric liquid crystal compound selectively reflects the specific wavelength can be fixed by rapidly cooling the compound from the liquid crystal phase temperature region to a solid phase temperature region. This is a characteristic that makes the compound effective as a material for reversible thermal recording media.
For this type of reversible thermal recording media, the temperature of heating from the recording head is controlled to thereby obtain desired colors. Although various types have been provided as image recording apparatuses having a recording head for heating, an apparatus is absent in which the heating time can be controlled and that is suitable for image recording onto reversible thermal recording media containing the cholesteric liquid crystal compound.
Accordingly, an object of the present invention is to provide an image recording apparatus and an image recording method capable of recording an image efficiently in desired colors onto a reversible thermal recording medium having a thermal recording layer containing the cholesteric liquid crystal compound.
According to an experiment performed by the present inventors, it was found that not only the heating time varies among the developed colors but also the most suitable heating time varies according to the kind of the liquid crystal material, the thickness of the recording layer and the like even when the same color is printed.
In light of the above-mentioned finding, the present invention was devised. Specifically, an image recording apparatus reflecting one aspect of the present invention comprises: a recording head for heating a reversible thermal recording medium that has a thermal recording layer containing a cholesteric liquid crystal compound to a predetermined temperature; and a speed control unit which is capable of changing a relative print feeding speed of the recording head and the reversible thermal recording medium.
In the image recording apparatus having the above-described structure, the quantity of heat applied from the recording head can be represented by the product of the consumed power and the heating time. The heating time is controlled by the relative print feeding speed of the recording head and the recording medium. Therefore, by changing the print feeding speed according to the kind of the reversible thermal recording medium (the kind of the liquid crystal, the thickness of the liquid crystal layer, the material and the thickness of the protecting layer and the base material, etc.), color development and the like, an image can be recorded in a desired color development condition with high quality.
After stopped at a position of an intended print pixel and heated to a predetermined temperature for printing, the recording medium and the recording head are stopped for a predetermined time to maintain heating at that temperature. In the present invention, the quotient when the predetermined time is divided by the distance of movement will be called a print feeding speed.
The image recording apparatus according to the present invention may have a sensor that detects the kind of the reversible thermal recording medium. By providing such sensor, recording can be performed reliably at a recording speed most suitable for the recording medium. When the sensor is one that detects the thickness of the recording medium and/or a mark previously provided on the recording medium, the kind of the recording medium can be grasped easily and reliably. An operation member for manually changing the print feeding speed may be provided.
Further, in the image recording apparatus according to the present invention, a detector that detects the condition of colors printed by the recording head may be provided so that the result of the detection by the detector is fed back to the speed control unit. By providing the detector and feeding back the result of the detection, more precise color development can be performed.
Further, a temperature control unit that makes the heat generation temperature of the recording head variable may be provided. By making the heat generation temperature variable, more precise color development can be performed.
According to another aspect of the present invention, a first image recording method comprises the steps of: determining a kind of a reversible recording medium that has a thermal recording layer containing a cholesteric liquid crystal compound; setting a recording speed according to the determined kind of the reversible thermal recording medium; and recording an image onto the reversible thermal recording medium by heating the reversible thermal recording medium to a predetermined temperature with the set recording speed. By setting or changing the recording speed according to the kind of the recording medium, an image can be recorded in a desired color development condition with high quality.
A second image recording method reflecting still further aspect of the present invention comprises:
determining a color development condition of a reversible recording medium that has a thermal recording layer containing a cholesteric liquid crystal compound; setting a recording speed according to the determined color development condition the reversible thermal recording medium; and recording an image onto the reversible thermal recording medium by heating the reversible thermal recording medium to a predetermined temperature with the set recording speed. By setting the recording speed according to the color development condition of the recording medium, an image can be recorded in a desired color development condition with high quality.
In addition to the recording speed, the heat generation temperature of the recording head may also be changed. By doing this, finer color development control can be performed.